A. Field
This invention relates to a method and apparatus for checking value documents having an authenticity feature in the form of at least one luminescent substance, the value document being irradiated with light and the luminescence radiation emanating from the value document being detected with spectral resolution to determine whether the authenticity feature is actually present in the checked value document.
B. Related Art
According to the present invention, a luminescent, e.g. fluorescent or phosphorescent, authenticity feature will be understood to be a single substance or a mixture of a plurality of substances showing luminescent behavior.
There are a number of known systems for checking the authenticity of such value documents. One system is known for example from the applicant's DE 23 66 274 C2. In this system the authenticity of a bank note is checked, i.e. it is specifically checked whether a fluorescent authenticity feature is actually present in a bank note to be checked, by irradiating said note and detecting the remitted fluorescence radiation with spectral resolution. Evaluation is done by comparing the signals from different photocells of the spectrometer.
This method works very reliably in most cases, but in particular when there are a plurality of possible authenticity features having very similar spectral behavior, it may be difficult to distinguish them and thus decide which of said authenticity features is actually present in the checked value document.
On these premises it is the problem of the present invention to provide a method and apparatus for checking value documents which make it possible to distinguish authenticity features with a similar spectral pattern in a simple and reliable way.